Filter Apparatus

ABSTRACT

The invention relates to a filter apparatus for depositing impurities from a fluid stream by means of use of a filter element ( 10 ) which is accommodated in a filter casing ( 12 ). By virtue of the filter casing ( 12 ), according to the characterizing part of claim  1 , having a swirl space ( 14 ) such that the fluid stream to be filtered is conducted at least partly in a swirling flow around the filter element ( 10 ), the properties of a cyclone are utilized for the actual filtration operation to the extent that the swirl space of the filter casing brings about multiple deflection of the direction of motion of the fluid to be filtered.

The invention relates to a filter apparatus for separating impurities from a fluid stream by using a filter element which is accommodated in a filter housing.

Similar hydraulic filters and filter apparatus are readily available on the market in a plurality of embodiments (DE 197 11 589 A1). In addition to suction filter apparatus, filter apparatus as return line filters, in-line filters, or ventilation filters are known. In generic terms they are often referred to as hydraulic filters. Generally it applies that these hydraulic filters are devices for separation of solids, fibrous, grainy, or lattice-shaped filter media being used to separate solids from liquids or for separating dusts from gases.

Furthermore, other separation devices in the prior art (DE 42 14 324 A1) are so-called cyclones which are devices with which the action of a centrifugal force separates particles of solids from gases or liquids which are subsumed in the jargon under the generic term fluid. In the aforementioned solution the cyclone is located in a ventilation path which leads from a driving mechanism space (crank space) to the intake line of an internal combustion engine so that aerosols entrained by the air are separated in the cyclone and can be delivered by way of an outlet to an oil sump of the internal combustion engine. In order to be able to prevent unwanted feed of oil from the oil sump into the cyclone even under extreme operating conditions there is a stop safeguard in the form of a float valve on the outlet side.

This cyclone separation technology has also already been used in combination with filter devices. Thus DE-OS 37 35 106 discloses a process for separating liquid particles from gases, in particular in the form of aerosols from exhaust gases, in which the gases are centrifuged first and then filtered. Some of the filtrate gases are then relayed to a cyclone and the liquid particles entrained in the gas flow are combined into droplets by frequent deflection of the direction of their motion (swirling flow) and the droplets emerge by their own weight from of the separation device.

Furthermore, U.S. Pat. No. 6,129,775 A discloses a cyclone separator with a predominantly conically running separation housing in which, following the wall of the separation housing and with the formation of a swirl space spaced analogously, there is a usually self-contained guide body which enables improved swirl guidance for separating the particles in the swirl space for a tangentially supplied fluid flow with particle fouling. Filtration by means of a filter element is not possible with the known solution.

The prior art (EP 06 59 462 A 1) also discloses solutions in which, for further particle separation, in the bypass flow of a cyclone separator a filter element is held in a separate filter housing which follows in the direction of the fluid stream. The filtration line of these known solutions still leaves much to be desired.

Proceeding from this prior art, the object of the invention is to devise a filter apparatus with improved filtration properties. This object is achieved by a filter apparatus with the features of claim 1 in its entirety.

In that, as specified in to the characterizing part of claim 1, the filter housing has a swirl space such that the fluid stream which is to be filtered is routed at least partially around the filter element in a swirling flow, for actual filtration operation the properties of the cyclone are used in so far as the swirl space of the filter housing causes repeated deflection of the direction of motion of the fluid to be filtered, the associated swirling flow being able to be established along the entire filter surface of the filter element, with the result that the fluid stream to be filtered passes through the filter element to an increased degree and with high energy input, with simultaneous retention or separation of impurities. The swirling flow achieved in the filter housing caused by the action of the swirl space yields a laminar, helix-like fluid flow which in contrast to the otherwise conventional radial throughflow of the filter element transversely to its longitudinal axis leads to improved filtration performance and results. In this way an increased throughput rate of the fluid to be filtered through the filter element can be achieved.

In one preferred embodiment of the filter apparatus according to the invention, the swirl space is formed by a conical widening of the filter housing in the direction of its one housing end, the feed inlet for the unfiltered medium extending through the filter housing off-center to the longitudinal axis of the filter element. This off-center feed causes improved generation of a cyclone-like flow under the action of the swirl space in the filter housing.

The conical widening of the filter housing in the region of the swirl space preferably undergoes transition into a cylindrical housing part or into one with a small conical tilt, with the result that partial damping of the swirl-like fluid flow occurs with reduced wall distances between the outside of the filter element and the inside of the filter housing, so that a kind of forced guidance for the purpose of a compressed fluid flow results in order to increase the feed amount of fouled fluid for the filter element in this way.

In another preferred embodiment of the filter apparatus according to the invention, with a definable axial distance above on the free end of the filter element a collecting space adjoins which likewise contributes to making the fluid flow uniform in the upper region, and helps prevent supercritical turbulences within the fluid flow; this otherwise could adversely affect the filtration performance of the filter apparatus.

It has proven especially advantageous with respect to the described structure of the filter housing to use as filter elements those whose filter element runs conically. It has also proven especially advantageous to use so-called slit screen tube filter elements as filter elements.

The filter apparatus according to the invention is detailed below using one embodiment. The figures are schematic and not to scale.

FIG. 1 shows a perspective view of the filter apparatus after making a middle longitudinal cut;

FIG. 2 shows a perspective view of the filter apparatus as shown in FIG. 1 in the state closed on the housing side and in another viewing direction.

The filter apparatus according to the invention is used to separate impurities from a fluid stream, for example formed by a hydraulic medium. But fundamentally the filter apparatus can also be used for gaseous media, aerosols, etc., which likewise form fluids in this way. FIGS. 1 and 2 correspond to the conventional installation direction, and to the extent the terms “top” and “bottom” are used below in this respect, they relate to the representations of the operating situation of the filter apparatus as shown in FIGS. 1 and 2.

The filter element 10 shown in FIG. 1 is accommodated by a filter housing 12 of the filter apparatus. The filter housing 12 on its top end has a swirl space 14 which is used to route the fluid to be filtered at least partially in a swirling flow or cyclone flow around the filter element 10. In the illustrated solution the swirl space 14 is formed by a conical widening of the filter housing 12 in the direction of its top end 16. Instead of this conical widening produced by the housing wall, in addition or as an alternative, on the inside of the filter housing 12 flow baffles—also in the manner of turbulators—(not shown) could be used. To produce the indicated swirling flow, the feed inlet 18 for the unfiltered media is located off-center to the longitudinal axis 20 of the filter element 10 and in this respect extends through the housing wall on the top end of the swirl space 14. To the outside the feed inlet 18 is provided with a flange-like widening 22 which is used to connect other fluid-carrying pipe elements or other line elements which are not shown.

After the fluid to be filtered flows from the outside to the inside through the filter element 10, the filtrate stream, that is, the filtered fluid, is withdrawn from the filter housing 12 via the drain 24 in the housing bottom. The free end of the drain 24 is in turn provided with a flange 26 which is used like the flange 22 to connect fluid-carrying lines to the filter apparatus. The drain 24 is placed on the top end of the filter housing 12 and, viewed in cross section, has a slightly larger cross section than the top fluid exit site 28 out of the filter housing 12. The indicated feed inlets and drains 18 and 24 can optionally be produced in one piece together with the filter housing 12; but the corresponding connection to the remaining filter housing 12 is possible by way of weld connections.

As furthermore follows especially from FIG. 1, the conical widening which forms the swirl space 14 undergoes transition in the direction of the bottom of the filter apparatus into a cylindrical housing part 30 which can also have a smaller conical tilt (not shown) opposite the swirl space 14. The swirling flow produced in the swirl space 14 is made uniform over the further housing part 30 in terms of the progression of the cyclone; this promotes fluid passage through the filter element 10. The cross sectional reduction from the swirl space 14 to the housing part 30 also contributes to this. The free end 32 of the filter element 10 is oriented in the direction of the closed end 34 of the filter housing 12 which forms at a definable axial distance to the filter element 10 a kind of collecting space 36 which, in spite of the partially turbulent flow dictated by the swirl space 14, leads to more uniformity of the fluid stream which penetrates the filter element 10 and otherwise produces good filling in the interior 38 of the filter housing 12; this promotes energy-efficient operation of the filter apparatus.

In particular, in this way fluid-free cavities do not form within the filter apparatus; this otherwise could lead to damaging cavities for the hydraulic circuit which is connected to the filter apparatus in operation. The closed end 34 can also be produced by way of a switch fitting 40 (cf. FIG. 2) which, for example, made as a ball valve enables opening of the bottom end of the filter housing 12. In this way, for example, it would be possible, with the switch fitting 40 closed, to carry out the already described filtration operation and when the bottom end of the filter housing 12 is opening, for example, the impurities which arise in a backflushing process to be carried out thus could be discharged from the filter apparatus. In the pertinent backflushing operation, cleaned fluid is routed from the inside to the outside through the filter element, preferably from the clean side of the filter apparatus, that is, coming from the drain 24; this leads to cleaning of the passages in the filter element 10 and the dirt which has been backflushed in this way could then be discharged from the filter apparatus by way of the interior 38 of the filter housing 12 and by way of the lower bottom opening of the filter housing 12.

But fundamentally there is also the possibility of backflushing for a housing situation as shown in FIG. 1 in which then the cleaned fluid is backflushed from the clean side (drain 24) in the direction of the unfiltered material side (feed inlet 18), and then the delivery of unfiltered material would have to be stopped. With a somewhat smaller tilt than applies to the housing wall of the swirl space 14, the collecting space 36 tapers likewise conically in the direction of the free or closed end 34 of the filter housing 12. This conical tapering allows a partial pressure rise in the collecting space 36 for operation of the apparatus; this promotes complete filling for the filter apparatus.

The filter element 10, as already addressed, is made as a slit screen tube filter element; DE 197 11 589 shows the more detailed structure of such a slit screen tube filter element. This element 10 consists of individual supports bars around which a wire profile is wound in individual turns, leaving exposed gaps through which fluid can pass, there being a weld in the region of each contact site of the wire profile with the assignable support bar. For improved filtration operation the filter element 10 is made conical, the turns of the wire profile decreasing in diameter in the direction of the tilted ends of the support bars and the length of the slit screen tube filter element measured in the direction of the longitudinal axis 20 being roughly 11 times greater than the largest exit cross section in the region of the outlet or drain 24. Since slit screen tube filter elements are fundamentally prior art, the pertinent element 10 in FIG. 1 is shown only in terms of its conical structure.

The conical structure of the slit screen tube filter element 10 results in less resistance being offered to the fluid stream which enters the housing 30 from the swirl space 14 relative to a solution with an exclusively cylindrically made element, with the result that the pressure difference for the entire filter apparatus is reduced in an energy-efficient manner and a constant liquid stream is achieved by the conical structure when the element 10 is backflushed, conversely for a cylindrical element (not shown) which could likewise be used in this embodiment the speed in its longitudinal direction continuously increases; this opposes uniform entry into the interior of the filter element.

The installation conditions are implemented such that viewed in the longitudinal direction (longitudinal axis 20) of the filter element 10, the overall length of the swirl space 14 with its conical housing wall 16 and of the collecting space 36 corresponds to a least one third, but less than half of the installation length of the filter element 10, the overall length of the swirl space 14 corresponding essentially to the overall length of the collecting space 36 which extends from the end 32 of the filter element 10 to the end 34 of the filter housing 12.

The filter apparatus according to the invention, in particular when it is built essentially in one piece except for the filter element 10, can be extremely economically produced and therefore operated as a disposable article. Depending on the pressures which arise, the filter apparatus can also be made as a plastic injection molding or can consist of metallic materials including sheet metal and casting materials, and the housing wall 16 of the swirl space 14 can be made as a dished bottom.

In a further configuration of the filter apparatus according to the invention which is not shown, it can be additionally provided that potential light floating materials may be removed from the filter housing via another outlet site in the region of the top housing end 16 of the filter housing 12 with formation of a kind of overflow line. Preferably the respective sealing opening relative to the longitudinal axis 20 is diametrically opposite the feed inlet 18 and the overflow line, comparably to the other connection sites, can have a corresponding flange body, as shown. 

1. A filter apparatus for separating impurities from a fluid stream by using a filter element (10) which is accommodated in a filter housing (12), characterized in that the filter housing (12) has a swirl space (14) such that the fluid stream to be filtered is routed at least partially around the filter element (10) in a swirling flow.
 2. The filter apparatus according to claim 1, wherein the swirl space (14) is formed by a conical widening of the filter housing (12) in the direction of one of its two housing ends (16) and that the feed inlet (18) for the unfiltered medium extends through the filter housing (12) off-center to the longitudinal axis (20) of the filter element (10).
 3. The filter apparatus according to claim 1, wherein the drain (24) for the filtered fluid extends through one housing end (16) and establishes a fluid connection to the interior of the filter element (10).
 4. The filter apparatus according to claim 2, wherein the conical widening of the filter housing (12) in the region of the swirl space (14) undergoes transition into a cylindrical housing part (30) or into one with a small conical tilt.
 5. The filter apparatus according to claim 4, wherein the free end (32) of the filter element (10) is oriented in the direction of the other end (34) of the filter housing (12) which forms a kind of collecting space (36) at a definable axial distance to the filter element (10).
 6. The filter apparatus according to claim 5, wherein the collecting space (36) tapers conically at least partially in the direction of the other end (34) of the filter housing (12).
 7. The filter apparatus according to claim 1, wherein the filter element (10) made preferably as a slit screen tube filter element tapers conically proceeding from the swirl space (14) to the free end (32).
 8. The filter apparatus according to claim 1, wherein the overall length of the swirl space (14) viewed in the longitudinal axis (20) of the filter element (10) with its conical housing wall (16) and of the collecting space (36) correspond to a least one third, but less than half of the installation length of the filter element (10). 